Image forming apparatus with constant conveying velocity

Abstract

An image forming apparatus includes plurality image carriers sequentially arranged, a conveying belt, which conveys a print medium onto which color-separated images formed on the plurality of image carriers are overlapped, and a plurality of image transfer rollers installed to respectively correspond to the plurality image carriers. The conveying belt is interposed between the image transfer rollers and the image carriers. At least one of the plurality image transfer rollers is arranged to be compressed with a pressure higher than those applied to the other image transfer rollers against the image carriers.

1. An image forming apparatus, comprising:
 a plurality of sequentially arranged image carriers; 
 a conveying belt which conveys a print medium onto which color-separated images formed on the plurality of image carriers are overlapped; and 
 a plurality of image transfer rollers installed to respectively correspond to the plurality of image carriers with the conveying belt being interposed between the image transfer rollers and the image carriers, 
 wherein with reference to a conveying direction of the print medium, an image transfer roller located at a most upstream side is compressed with a pressure higher than those applied to the other image transfer rollers. 
 
   
   
     2. An image forming apparatus as claimed in  claim 1 , wherein if the plurality of image transfer rollers are respectively called as a first to a fourth image transfer rollers in sequence from the upstream side to the downstream side of the conveying direction of the print medium, the pressure which compresses the first image transfer roller against the corresponding image carrier is higher than the pressure exerted to compress the second image transfer roller. 
   
   
     3. An image forming apparatus, comprising:
 a plurality of sequentially arranged image carriers; 
 a conveying belt which conveys a print medium onto which color-separated images formed on the plurality of image carriers are overlapped; and 
 a plurality of image transfer rollers installed to respectively correspond to the plurality of image carriers with the conveying belt being interposed between the image transfer rollers and the image carriers, 
 wherein at least one of the plurality of image transfer rollers is arranged to be compressed with a pressure higher than those applied to the other image transfer rollers against the plurality of image carriers, 
 if the plurality of image transfer rollers are respectively called as a first to a fourth image transfer rollers in sequence from the upstream side to the downstream side of the conveying direction of the print medium, the pressure which compresses the first image transfer roller against the corresponding image carrier is higher than the pressure exerted to compress the second image transfer roller, and 
 the pressure which compresses the second image transfer roller against the corresponding image carrier is higher than the pressures which compresses the third and fourth image transfer rollers. 
 
   
   
     4. An image forming apparatus as claimed in  claim 2 , wherein the pressure which compresses the first image transfer roller is not less than about 2.5 times of the pressure which compresses the third image transfer roller. 
   
   
     5. An image forming apparatus, comprising:
 a plurality of sequentially arranged image carriers; 
 a conveying belt which conveys a print medium onto which color-separated images formed on the plurality of image carriers are overlapped; and 
 a plurality of image transfer rollers installed to respectively correspond to the plurality of image carriers with the conveying belt being interposed between the image transfer rollers and the image carriers, 
 wherein at least one of the plurality of image transfer rollers is arranged to be compressed with a pressure higher than those applied to the other image transfer rollers against the plurality of image carriers, 
 if the plurality of image transfer rollers are respectively called as a first to a fourth image transfer rollers in sequence from the upstream side to the downstream side of the conveying direction of the print medium, the pressure which compresses the first image transfer roller against the corresponding image carrier is higher than the pressure exerted to compress the second image transfer roller, and 
 the pressure which compresses the second image transfer roller is not less than about 1.5 times of the pressures which compresses the third image transfer roller. 
 
   
   
     6. An image forming apparatus as claimed in  claim 1 , further comprising a compression unit to elastically compress the ends of the plurality image transfer rollers. 
   
   
     7. An image forming apparatus as claimed in  claim 6 , wherein the compression unit comprises:
 a plurality of axle supporting members which support axles of the image transfer rollers, respectively; and 
 a plurality of elastic members to independently and elastically compress the axle supporting members, respectively. 
 
   
   
     8. An image forming apparatus as claimed in  claim 7 , wherein at least one of the plurality of elastic members supplies an elastic force different in magnitude from those of the other elastic members. 
   
   
     9. An image forming apparatus, comprising:
 a plurality of sequentially arranged image carriers; 
 a conveying belt which conveys a print medium onto which color-separated images formed on the plurality of image carriers are overlapped; 
 a plurality of image transfer rollers installed to respectively correspond to the plurality of image carriers with the conveying belt being interposed between the image transfer rollers and the image carriers; and 
 a compression unit to elastically compress the ends of the plurality image transfer rollers; 
 wherein at least one of the plurality of image transfer rollers is arranged to be compressed with a pressure higher than those applied to the other image transfer rollers against the plurality of image carriers, 
 the compression unit comprises
 a plurality of axle supporting members which support axles of the image transfer rollers, respectively, and 
 a plurality of elastic members to independently and elastically compress the axle supporting members, respectively, and 
 
 the plurality of elastic members are installed sequentially in such a way that with reference to the conveying direction of the print medium, an elastic member located at the upstream side exerts a higher pressure than any other elastic member located at the downstream side. 
 
   
   
     10. An image forming apparatus as claimed in  claim 1 , further comprising a charging member installed upstream of the plurality of image carriers with reference to the conveying direction of the print medium to produce static electricity on the print medium. 
   
   
     11. An image forming apparatus, comprising:
 a plurality of sequentially arranged image carriers; 
 a conveying belt which conveys a print medium onto which color-separated images formed on the plurality of image carriers are overlapped; 
 a plurality of image transfer rollers installed to respectively correspond to the plurality of image carriers with the conveying belt being interposed between the image transfer rollers and the image carriers; and 
 a charging member installed upstream of the plurality of image carriers with reference to the conveying direction of the print medium, to produce static electricity on the print medium, 
 wherein at least one of the plurality of image transfer rollers is arranged to be compressed with a pressure higher than those applied to the other image transfer rollers against the plurality of image carriers, and 
 the charging member comprises a charging roller installed to move into and out of contact with and be rotated by the conveying belt. 
 
   
   
     12. An image forming apparatus as claimed in  claim 6 , further comprising an charging member installed upstream of the plurality image carriers with reference to the conveying direction of the print medium to produce static electricity on the print medium. 
   
   
     13. An image forming apparatus, comprising:
 a plurality of sequentially arranged image carriers; 
 a conveying belt which conveys a print medium onto which color-separated images formed on the plurality of image carriers are overlapped; and 
 a plurality of image transfer rollers installed to respectively correspond to the plurality of image carriers with the conveying belt being interposed between the image transfer rollers and the image carriers, 
 wherein at least one of the plurality of image transfer rollers is arranged to be compressed with a pressure higher than those applied to the other image transfer rollers against the plurality of image carriers, and 
 the pressure exerted to the most weakly compressed image transfer roller among the plurality of image transfer rollers is the minimum transfer pressure required to transfer the images of the image carriers. 
 
   
   
     14. An image forming apparatus, comprising:
 a plurality of sequentially arranged image carriers; 
 a conveying belt that conveys a print medium onto which color-separated images formed on the plurality of image carriers are overlapped; and 
 a plurality of image transfer rollers installed to respectively correspond to the plurality of image carriers with the conveying belt being interposed between the image transfer rollers and the image carriers, 
 wherein with reference to a conveying direction of the print medium, a pressure that compresses a most upstream image transfer roller against the corresponding image carrier is higher than a pressure that compresses a second-most upstream image transfer roller against the corresponding image carrier, which is higher than the pressures that compress the remaining image transfer rollers.